This invention relates to alignment tapes for magnetic recording and playback devices and devices for producing the same. More particularly, the invention relates to an alignment tape for aligning the linearity of tracks in magnetic recording and playback devices, which create tracks using a rotating head, as used for example, in digital audio tape recorders (DAT), 8 mm video tape recorders and VHS type video tape recorders.
Conventional helical scan magnetic recording and playback devices include digital audio tape recorders (DAT) and 8 mm video tape recorders. In these helical scan magnetic recording and playback devices, a magnetic tape is driven forward and wound at a specified angle around a drum rotating at a high speed, having magnetic heads fixed thereon.
In order to perform high-density recordings, a pair of magnetic heads (head A and head B) with differing azimuth angles (.alpha.) are fixed on a rotating drum displaced 180.degree. from each other about the circumference of the rotating drum. Head A is set with azimuth angle .alpha.=+20.degree. and head B with azimuth angle .alpha.=-20.degree.. The magnetic heads record on alternating tracks. Tracks recorded by one of the heads lie adjacent to the tracks recorded by the other of the heads.
Referring to FIG. 9(A), the track format of such a high-density recorded tape is shown. Tracks 2a are recorded by one of the heads with an azimuth angle of +20.degree.. . Tracks 2b are recorded by the other head with an azimuth angle of -20.degree.. The 40-degree difference in azimuth angles between tracks 2a and 2b reduces adjacent-track interference when reproducing the recorded information.
Referring now also to FIG. 9(B), a detailed view of a prior art high-density track format shows heads A and B (broken lines) and their relationship to two adjacent tracks 2a and 2b with azimuth angles .alpha.=+20.degree. and -20.degree. respectively. Arrows indicate the directions of tape and head travel.
Referring now to FIG. 10, a conventional alignment tape for aligning a helical scan magnetic includes an alignment track 2a on a magnetic tape 2. Alignment track 2a is recorded according at a skew angle specified by DAT standards (indicated by the upward sloping arrow). The signal is recorded at a frequency that permits the playback envelope waveform to be easily observed (normally about 2.35 Mhz). For purposes of alignment, magnetic tape 2 need not be recorded with every track filled. In fact, if every track were recorded, adjacent-track interference of such a high-density recording interferes with accurate observation of the playback envelope waveform. Consequently, alignment track 2a is recorded only by head A having an azimuth angle, .alpha.=+20.degree.. The intervening tracks, normally recorded by head B remain blank. In this way, every other track is recorded by the same magnetic head with the same azimuth angle of =+20.
It should be noted that the rotating drum may have either two heads or four heads.
Referring now to FIG. 12(a), rotating drum 7 includes two heads A and B located 180.degree. from each other about the circumference of rotating drum 7. Heads A and B are used for both recording and playback.
Referring now to FIG. 12(b), a rotating drum 7' includes four heads A, B', B and A' 90 degrees apart about the circumference of rotating drum 7'. Heads A and B, located 180.degree. apart, are used only for recording. Heads A' and B', also located 180.degree. apart are used only for playback. Playback heads A' and B' are offset from recording heads A and B by 90.degree..
Referring now to FIG. 7, a typical DAT tape path is shown. A magnetic tape 2 is drawn out from a supply side reel 1a. Magnetic tape 2 is guided to give 90.degree. of mobile contact between its surface and a peripheral surface of a rotating drum 7. On the upstream side, magnetic tape 2 is guided by a supply side stabilizing post 3a, a tension post 4, an incoming side guide roller 5a, and an incoming side inclined post 6a. On the downstream side magnetic tape 2 is guided by an outgoing side inclined post 6b, an outgoing side guide roller 5b, a capstan 8 opposed by a pinch roller 9 and a take-up stabilizing post 3b to a take-up reel 1b.
More specifically, supply side stabilizing post 3a maintains magnetic tape 2 at a fixed angle with respect to tension post 4, regardless of changes in the take-up quantity of magnetic tape 2 from supply side reel 1a. Tension post 4 is spring-loaded to maintain a constant tension in magnetic tape 2 by moving in accordance with the changes of tension in magnetic tape 2.
Capstan 8 and pinch roller 9 provide the driving force for magnetic tape 2. Capstan 8 rotates against a surface of magnetic tape 2 squeezed against pinch roller 9 to draw magnetic tape 2 toward take-up reel 1b. Take-up side stabilizing post 3b maintains a fixed angle of magnetic tape 2 with respect to an axis of capstan 8 and pinch roller 9, regardless of the amount of magnetic tape wound on take-up reel 1b.
Referring now also to FIGS. 8(A) and 8(B), the contact position and contact angle of magnetic tape 2 against rotating drum 7 is determined by incoming side guide roller 5a, incoming side inclined post 6a, outgoing side inclined post 6b and outgoing side guide roller 5b.
In the prior art device described, rotating drum 7 has a diameter of 30 mm and a contact angle of magnetic tape 2 against rotating drum 7 of 90.degree.. A rotation axis of rotating drum 7 is inclined at an angle of 7.degree. 50' to the travel direction of magnetic tape 2. This inclination creates an inclined track.
Magnetic tape 2 is maintained in full contact with the peripheral surface of rotating drum 7, aligned at the desired contact position and contact angle, by incoming side guide roller 5a, incoming side inclined post 6a, outgoing side inclined post 6b and outgoing side guide roller 5b.
In these types of helical scan magnetic recording and playback devices, it is essential that the material recorded be accurately laid down on the tracks in accordance with the proper format and that upon playback, the recorded tracks be accurately tracked. For these reasons, the angle and vertical positioning of the tape path against rotating drum 7 has to be precise. Various factors, including manufacturing tolerances, may degrade accurate alignment following assembly of the recorder. The device may therefore require further adjustment to correct the alignment.
Alignment is controlled by the path alignment mechanism to maintain the correct tape path. The tape path is aligned by moving incoming side guide roller 5a and outgoing side guide roller 5b up and down until the desired tape path is attained. Shafts of incoming side guide roller 5a and outgoing side guide roller 5b are screws which permit loosening, repositioning of their respective guide rollers 5a and 5b, and then tightening.
Referring now also to FIGS. 11(A) and 11(B), an envelope waveform of the playback signal produced by an alignment tape indicates the nature of the adjustment to be performed on incoming side guide roller 5a and outgoing side guide roller 5b to properly align the tape mechanism.
Referring specifically to FIG. 11(A), the envelope waveform of a playback signal is shown produced by a properly aligned magnetic head. A solid line indicates an on-track state and a dashed line indicates an off-track state. The magnetic head scans the specified track from entry to exit, to produce a flat envelope waveform.
Referring now to FIG. 11(B), an envelope waveform of a playback signal is shown that is produced by magnetic head reproducing a signal from a misadjusted tape path, and in which alignment of the tape path is necessary. The solid line indicates an on-track state and the dashed line indicates an off-track state. The magnetic head gradually shifts from alignment with the track at track entry, to misalignment at track exit. The amplitude of the playback signal thus diminishes from high amplitude at entry to low amplitude at exit. An opposite situation is possible wherein the magnetic head enters the track misaligned and reaches substantial alignment at exit. The track angle of the magnetic tape is adjusted so that the track angle is aligned with the tracks of the alignment tape by adjusting the heights of incoming side guide roller 5(a), or outgoing side guide roller 5(b), or both.
As shown above, prior art alignment tapes for magnetic recording and playback devices have an alignment track created every other track. Since the alignment track intervals are small, the adjacent track may be played back during an off-track state, as shown by the dotted lines in FIGS. 11(A) and 11(B). A relatively large playback signal is displayed on an oscilloscope as a result of mixing on-track and off-track signals. Thus, despite the fact that alignment tracks are recorded on every other track, a strong signal interference still exists between adjacent alignment tracks. This makes it difficult to use the displayed envelope waveform for aligning the tracks.